Perfume won’t protect you from mosquito bites

VictorissecretThe headlines have been awash with claims that a popular perfume may repel as many mosquitoes as those regularly recommended by health authorities. Could it be true?

In short, no. There is little surprise that the results of this recently published study in the Journal of Insect Science has attracted so much attention. Everyone loves the idea that some unexpected substance could be used as a mosquito repellent. Even better if it performs as well, or even better, than those such as DEET or picaridin that are widely recommended by health authorities.

The scientists tested a range of commercial insect repellents. Three formulations of DEET based repellent, an oil of lemon eucalyptus (aka PMD) based repellent, three botanical-based repellents, a mosquito repellent patch (Vitamin B), a product not specifically designed as a repellent but often quoted as being effective (Avon skin so soft) and the perfume. Why include the perfume at all?

The logic behind including the perfume was a good one. It is often said that floral perfumes and other cosmetics attract mosquitoes. I’ve never thought this is actually the case. I mean, there is stronger evidence that mosquitoes re attracted to smelly foot bacteria than pleasant smelling cosmetics! I always suspected that the idea comes from the fact the mosquitoes (mostly the non-biting males) will feed on plant sugars. However, it was worth including in this study. Always good to gather some quantitative evidence on the response of blood-seeking mosquitoes. It could be a good opportunity to bust (or perhaps confirm) some urban myths.

I’ve written before about how you can test mosquito repellents. While the “arm-in-cage” methodology typically provides the best indication of how a mosquito repellent will perform, there are other methods commonly employed. In this case, the researchers used a “Y-tube” setup. This system basically allows mosquitoes to make a choice as to whether they preferentially fly towards one or the other ends of the tube. If you insert a hand treated with a substance into one end and another untreated hand as a control into the other, it is possible to measure the overall repellent effect by tracking the movement of mosquitoes.

Firstly, it is interested to note that the researchers found that some mosquitoes were attracted to the hand treated with DEET. If I was conducting an “arm in cage” test. I would be very surprised if I had any mosquitoes biting a DEET-treated arm within 2h of application. In one study, I found an approximately 7% DEET-based repellent stopped bites for a little under 2h. It makes me wonder how many mosquitoes may fly up to tube towards the treated hand but, given the chance, would actually bite the hand?

Fewer mosquitoes were attracted to hands treated with oil of lemon eucalyptus, not surprising either given this product is regularly recommended as an effective repellent by health authorities.

The testing of the perfume provided the headline grabbing results! For the first couple of hours, there wasn’t much difference in the proportion of mosquitoes repelled by the perfume compared to the other repellents. Why? It may be related to the strength of the odour overpowering the sensory organs of the mosquito. I think this is how some strongly smelling essential oils can provide some protection. It masks the normal chemical cocktails of smells on our skin that attracts mosquitoes.

We all know how overpowering the smell of some cosmetics can be. In this case of this experiment, a relatively high dose of the products as used. The authors make note of this too when they state “It must be noted that the concentration of perfume we used in this test was rather high and that lower concentrations of the same fragrance might have different effects.”

Could this perfume be used as a repellent?

Studies like this provide some fun headlines but they can be misleading to the public. What “works” for a relatively short period in a small laboratory based study does not necessarily stand up the practicalities of real life.

Notwithstanding the expense (the perfume is about AUS$80 for 100ml compared to less than AUS$10 for about the same amount of DEET-based repellent) I must admit that for some of these products, the smell can be so overpowering that applying them to large areas of skin would probably be more unpleasant than the bites of mosquitoes!

When trying to help the public choose and use mosquito repellents more effectively, it is critical that health authorities stick to products that are currently registered for use as a mosquito repellent and that have been demonstrated to provide suitable protection from biting mosquitoes over extended periods of time.

Perhaps the most important finding of the paper is not that the perfume repelled some mosquitoes but that patches infused with Vitamin B provide absolutely no protection from mosquitoes. This is one urban myth that never really seems to go away!

We also know that Victoria’s Secret perfume doesn’t stop bed bugs invading lingerie stores!

[The image used at the top of this piece is taken from here.]

Are mosquito coils making us sick?

coilWe burn them to beat the bite of mosquitoes but could they actually be making us sick? Is breathing the smoke from a smouldering mosquito coil really the same as smoking a pack of cigarettes?

In summary, should I use mosquito coils to protect my family from mosquito bites?

  • Only use commercial products that have been registered by local authorities
  • Products that contain pyrethroids will provide better protection from mosquitoes than those that contain only botanical extracts
  • The byproducts of combustion, not insecticides, associated with mosquito coils may pose a health risk in some circumstances
  • Best to limit use of coils to outdoor or well ventilated indoor areas
  • Don’t sleep next to a smouldering mosquito coil
  • Consider plug-in “smokeless” mosquito repellent devices
  • Sleeping under a mosquito net is the best non-chemical approach to overnight mosquito bite prevention
The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

Here is the background…

For centuries we’ve burnt substances, particularly aromatic plants, to keep mosquitoes away. The clouds of smelly smoke can often ward off the swarms of blood sucking mosquitoes.

The use of pyrethrum in incense gained popularity and became common practice in Asia but it wasn’t until the early 1900s that the mosquito coil was born thanks to Japanese entrepreneurs Eiichiro and Yuki Ueyama and their katori senkō (mosquito-killing incense).

Modern mosquito coils, mostly containing the pyrethroid insecticides, are an almost permanent fixture at camp sites and backyard during summer. Millions of families across the tropics use them as their primary source of mosquito-borne disease prevention. They’re cheap and generally effective. We burn them to reduce the risks of mosquito-borne disease but could they actually be making us sick?

Health concerns of mosquito coils

There is growing concern about the adverse health impacts associated with the burning of mosquito coils and sticks indoors. A recently presentation to the 48th National Conference of Indian College of Allergy, Asthma and Applied Immunology has again raised the issue of potential health impacts associated with mosquito coils with media coverage given to Dr Sundeep Salvi in the lead up to the conference. He is quoted as saying “Burning one mosquito coil in a closed room amounts to smoking roughly 100 cigarettes”. The key point in Dr Salvi’s comment is “closed room”.

When assessing the real risks posed by mosquito coils, it is important to consider not just what is released by these smouldering products but actual likelihood it poses a serious health risk. How do you balance these potential health risks of burning coils with those posed by the bite of infected mosquitoes?

Total daily rainfall recorded at Sydney Olympic Park (Data source Bureau of Meteorology)

Do you really need to weigh up the risks of breathing in smoke from a mosquito coil with the risks of mosquito bites? (Image: Joel Sartore, National Geographic)

Who checks the safety of mosquito coils?

In Australia, all substances that purport to kill or repel mosquitoes must be registered by the Australian Pesticides and Veterinary Medicines Authority (APVMA). Similar regulatory authorities exist in other jurisdictions.

Mosquito repellents, whether they’re topical or spatial or whether they contain “chemical” or “natural” substances will need to be tested for efficacy and safety. Check the packaging for a registration number. There are dozens of different variations on “mosquito coils” including sticks, coils, candles and a variety of “plug in” devices. You’ll find the shelves of the local supermarket, camping and hardware store fully stocked almost all year round!

Despite the wide range of products available, the active ingredients (that is the mosquito repelling or killing products) don’t vary too much. There are either synthetic pyrethroids or botanical extracts (e.g. citronella oil, eucalytpus oil). You may be surprised to know that some contain a combination of the two. Just because “citronella” is written in bold on the packaging, it may still contain one of the synthetic pyrethroids. Check the label.

repellentrackDoes burning mosquito coils really make us sick?

A study of mosquito coils sold in the U.S. and found that some mosquito coils contain octachlorodipropyl ether (s-2) that, during the smouldering of the coils, produces an extremely potent lung carcinogen as a byproduct called (bis(chloromethyl)ether (BCME)). Fortunately, s-2 is banned in many countries. It is no longer used commercially in the U.S. and prompted by reports of the risks associated with mosquito coils, Hong Kong authorities released a statement in 2005 regarding the recall of mosquito coils containing s-2.

It is not listed as an active ingredient in mosquito coils registered for use in Australia. Given that in most circumstances, particularly in Australia, mosquito coils don’t contain s-2, it is the particulate matter that is of greatest concern.

An often quoted study published in 2003 titled “Mosquito coil emissions and health implications” analysed the components of commercially available mosquito coils from China and Malaysia and found that burning mosquito coils in an enclosed room may pose “significant acute and chronic health risks” with the fine and ultra fine particulate matter released from a single mosquito coil equaling that of up to 137 cigarettes!

In addition, they found that emission of formaldehyde (a by product of the combustion process) from burning one coil can be as high as that released from burning 51 cigarettes.

Doesn’t sound too good does it? The combustion of the coil itself is the main concern, not the insecticides used.

More recent studies have indicated that changing the base materials used in mosquito coils (i.e. switching to charcoal from other organic material) can reduce the volume of particulate matter substantially. Would these “smokeless” mosquitoes be more “healthy”? Probably.

Does what happens in the lab stays in the lab?

Billions of mosquito coils are sold across Asia every year. Millions of families use them as their primary mosquito bite prevention strategy. Why aren’t we seeing more substantial health impacts in local communities?

It is worth noting that two papers published in 2006 investigated the different methods used to assess the health risks associated with burning mosquito coils. The researchers tested different methods to expose laboratory rats to particulate matter from mosquito coils. They firstly reported that “protocols devised evaluate and assess the acute inhalation toxicity of mosquito coil smoke demonstrating that the nose-only mode of exposure of rats to the smoke of mosquito coils is suitable to assess the toxic potency of different coils.

The nose-only mode has clear advantages over the whole-body exposure mode.” Then, using the “nose-only” exposure method that they proposed, the researchers concluded that “overnight exposure to the smoke from burning mosquito coils (manufactured in Indonesia) is unlikely to be associated with any unreasonable health risk.” This is a noteworthy conclusion given that the level of exposure to those rats (6 h a day, 5 days a week for 13 weeks) was substantial.

What about “smokeless” mosquito coils?

There is a paucity of studies investigating the potential human health impacts of “smokeless” mosquito repellents. The few studies that do exist are inconclusive or use animals to test health impacts under conditions unlikely to occur in most circumstances.

A 2005 review of pyrethroid poisoning reported “Despite their extensive world-wide use, there are relatively few reports of human pyrethroid poisoning. Less than ten deaths have been reported from ingestion or following occupational exposure. Occupationally, the main route of pyrethroid absorption is through the skin. Inhalation is much less important but increases when pyrethroids are used in confined spaces.” Again, this highlights the critical issue here, exposure to insecticides in confined and/or enclosed situations.

It is worth remembering that pyrethroids are over 2000 times more toxic to insects than mammals. That means that the concentrations used to kill insects are unlikely to have adverse health impacts on humans, particularly if commercial formulations are used as recommended. Given the billions of people who use mosquito coils to prevent mosquito bites, perhaps the more important question to ask is, does burning mosquito coils actually prevent mosquito-borne disease? Perhaps that is a discussion for another time….

sp-breweries-mozzie-boxPerhaps one of the most interesting ideas this year was the “mosquito repellent beer carton”. More marketing than public health initiative but I like the idea. The carton is infused with citronella so that when you’re sitting about the campfire enjoying a few beers, you can toss bits of the carton into the fire and keep mosquitoes away. It is unlikely many mosquitoes will be actively repelled. However, I do like the idea of using the beer carton as an opportunity to raise awareness of mosquito-borne disease.

Perhaps it is this little bit of public health communication that will actually stop a few people becoming infected.

Do you use mosquito coils and sticks to prevent mosquito bites? Join the conversation on Twitter and let me know what you think.

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.


Read more at The Conversation: Are mosquito coils good or bad for our health?


Read more at The Conversation: What can I eat to stop mosquitoes biting me?


Read more at The Conversation: The best (and worst) ways to beat mosquito bites



 

Why would a Californian drought trigger an outbreak of mosquito-borne disease?

CalifornianBushfireSunset_DawnEllnerMosquitoes need water almost as much as they need blood so why is it a drought could cause an outbreak of mosquito-borne disease? Why does the drought in California mean less water but more mosquito-borne disease?

More than just water

All mosquitoes need water. It could be a teaspoon of water in a pot plant base or an expanse of wetlands inundated by tides. Following flooding, health authorities are typically quick to issue public health warnings about increased risk of mosquito-borne disease. However, more mosquitoes doesn’t always mean more mosquito-borne disease.

Mosquitoes need blood. As well as biting people, they also bite animals. Outbreaks of mosquito-borne disease typically requires the presence of wildlife, animals that act as reservoirs for the disease-causing viruses.

CaliforniaDrought_EPA

Drought is hitting California hard (Source EPA via Huffington Post)

Mosquitoes, drought and West Nile virus

West Nile virus is a mosquito-borne pathogen generally spread between birds and people by mosquitoes. Culex mosquitoes they appear to play the most important role in West Nile virus transmission in urban environments, particularly Culex pipiens.

These mosquitoes are generally not breeding in wetlands. They’re found in artificial structures ranging from backyard containers and neglected swimming pools to stormwater pipes and drains. These mosquitoes have moved out of the swamps and into the suburbs! They’ve also moved into the constructed wetlands popping up throughout the suburbs too.

Rather than water birds associated with wetland environments, the birds playing a key role in West Nile virus transmission are small songbirds common in urban areas. These birds roost in large numbers and are the target the the Culex mosquitoes that preferentially feed on birds. It is important to keep in mind that there is still a lot of learn about how the roosting behaviour of birds influences their exposure to West Nile virus.

During “dry” conditions, bird populations are concentrated in urban areas (where humans provide water and food) and mosquito populations associated with urban water-holding structures increase. During “wet” summers, bird populations may be more widely dispersed through the environment with many birds roosting and foraging well away from residential areas and reducing the contact between birds, mosquitoes and people. When the “dry” summers arrive, birds move back close to the people. People who provide water.

Culex_molestus_Photo_StephenDoggett

The Culex pipiens group of mosquitoes play an important role in the transmission of West Nile virus and are closely associated with urban environments. They like biting birds. (Photo: Stephen Doggett, NSW Health Pathology)

In the absence of rain, water stagnates in stormwater pipes and drains providing favourable conditions for mosquitoes. During “wet” summers, the mosquitoes are flushed out by increased water flows and, even if they don’t, permanent habitats are more likely to support populations of mosquito predators such as fish.

During “dry” summers, people also start storing water around the home. Once water restrictions kick in, the desire to keep the garden looking healthy can potentially pose an indirect health risk to the homeowner as they hoard water around the home that provides habitat for mosquitoes.

In short, dry conditions help concentrate mosquitoes and birds in close proximity to people and increase the risk of mosquito-borne disease outbreaks.

WestNileSign

Mosquito control in Texas in response to an outbreak of West Nile virus raised much concern within the community. It can sometimes be difficult to balance the need for mosquito control with community engagement to allay fears of insecticide -based human health risks (Source: CDC)

An outbreak in Texas in 2012

West Nile virus was first introduced into North America in 1999. Despite rapidly spreading across the continent in the subsequent years, the numbers of outbreaks steadily declined and, to some extent, it fell of the radar as a serious public health concern. There was a resurgence of the disease in 2012 with an outbreak primarily focused in Texas.

There was a substantial increase in the number of cases compared to previous years with an unusually warm spring thought to have played an important role in driving the outbreak. Health authorities were warned that outbreaks of this nature may continue.

USDroughtMonitors_7April2015West Nile virus and the Californian drought

For the past couple of years, California has been hit with one of its worst droughts in decades. It is having widespread impacts and may also be increasing mosquito-borne disease. Californian authorities have been battling potential public health risks associated with mosquitoes on many fronts. There were record numbers of deaths due to West Nile virus disease in 2014 and exotic mosquitoes were detected. This included an Australian mosquito that was found in Los Angeles.

It is relatively early in California’s mosquito season but West Nile virus has already been detected. Health authorities are warning that another bad year for West Nile virus activity could be ahead despite the ongoing drought. There is already a suggestion that the severity of the current drought may be exacerbated by climate change and that climate change may be playing a role in future West Nile virus risk internationally.

There is little doubt that prolonged drought will impact Californian residents in many ways and an increased risk of mosquito-borne disease is just one of them. Fortunately, mosquito and vector control agencies in California work closely with local health authorities to monitoring mosquito and pathogen activity to provide warnings of increased risk. However, there is responsibility for everyone to ensure that the ways in which water is conserved around the home doesn’t increase the risks associated with mosquitoes.

potplantsaucer

If you’re worried about keeping your pot plants well watered but don’t want to provide a home for mosquitoes, fill the saucer with sand. It will keep the moisture in place but there is no “free water” for mozzies to use!

If you’re not able to “dump and drain” water holding containers, make sure that they’re covered to stop mosquitoes getting in or out. If you’ve got a swimming pool that’s neglected, start chlorinating it or release fish to eat through any mosquitoes. There are also a few mosquito control products that could be used, the most appropriate would probably be the insect growth regulator methoprene, it will stop mosquitoes emerging from the water holding container.

Why not share your tips on saving water around the home while not increasing opportunities for mosquitoes on Twitter?

The photo at the top of this post is taken by Dawn Ellner (see original photo here)

AMCA Meeting in Atlantic City

Dr Cameron Webb

Dr Cameron Webb visiting Cape May Department of Mosquito Control, February 2013

I had the pleasure of being invited to give a plenary lecture at the 79th Annual Meeting of the American Mosquito Control Association held in Atlantic City, NJ, in February. The annual meetings of the AMCA are typically large and busy events with over 800 delegates and industry sponsors.

The 2013 meeting was of particular interest for a couple of reasons. Firstly, it celebrated the 100th anniversary of the New Jersey Mosquito Control Association. New Jersey was the region where many of the most effective mosquito management strategies were developed, from habitat modification to community education and from pesticide development to research into personal insect repellents. Secondly, North American experienced one of their largest outbreaks of West Nile virus in 2012 and, in combination with work currently underway to manage the exotic dengue vector Aedes albopictus, the meeting promised to be filled with some interesting presentations. The full program is available here.

The title of my presentation was “Mosquito management in Australia: Emerging risks and environmental constraints”. I touched on many of the issues facing local authorities in Australia from the threats of exotic mosquitoes and pathogens, a change climate, urban development and wetland conservation. These issues are shared with many regions in North American, particularly Florida and California where residential developments are either encroaching on local wetlands or are constructing wetlands as part of stormwater management programs within these new developments.

The abstract of my presentation is below.

Mosquito-borne disease management in Australia faces challenges on many fronts.  Increasing coastal urbanisation is bringing the community closer to productive mosquito habitats but environmental management of coastal wetlands is often in conflict with effective mosquito control strategies. Concerns regarding the indirect impact of broadscale mosquito control on local insectivorous bat populations have resulted in a reluctance of authorities to approve control programs. As a result, local authorities are turning to urban planning strategies in an attempt to minimise the risks to the community. Extensive flooding of eastern states in association with prevailing La Nina weather patterns has seen the re-emergence of the potentially fatal Murray Valley encephalitis virus. In addition, a virulent strain of Kunjin virus has had significant veterinary impacts across eastern states. Over the same period, the south west coast of Australia experienced some of the highest rates of Ross River virus infection and local authorities struggled to manage unusually large estuarine mosquito populations. As the east coast returns to hot and dry summers in association with La Nino weather patterns, concerns are being raised as to the potential risks associated with Ross River virus and Barmah Forest virus as estuarine habitats become more suitable for pest and vector species. In addition to these potentially enhanced conditions, major estuarine wetland rehabilitation projects are underway that hold the potential to significantly increase the abundance of local mosquitoes. The risks associated with dengue transmission remain in Far North Queensland. There is much debate surrounding the potential introduction and spread of Aedes albopictus into mainland Australia in combination with predicted southern movement of Aedes aegypti. Water Sensitive Urban Design strategies are intended to increase water conservation through water storage in new residential developments. In combination with general water hoarding behaviour of the community during extended periods of below average rainfall, could we be creating conditions for potential dengue activity in our major metropolitan areas? These issues will be discussed and illustrated by local case studies.

As part of my visit, I had the opportunity to travel to the Cape May Department of Mosquito Control. The facility itself is close to 100 years old (although only a few buildings still remain from the “old days”) and was even used to house German POW during WWII. It was a pleasure to speak to Peter Bosak (Superintendent) and Ed Sokorai (Wetlands Specialist) about the issues they face in mosquito control throughout the extensive saltmarsh environments of southern New Jersey.